The present invention relates generally to rupturable pressure relieving apparatus and methods of manufacturing the same, and more particularly, but not by way of limitation, to an inverting, rupturable, pressure relieving apparatus having a predeterminable inversion initiation point and methods of manufacturing the same.
A variety of rupturable pressure relieving apparatus for containing fluids under pressure until a predetermined pressure level is exerted thereon have been developed and used heretofore. For example, battery cases and aerosol cans have included rupturable pressure relief areas or vents which function to relieve excessive fluid pressures from within the cases or cans. Also, rupture disk assemblies for containing pressurized fluids are commonly utilized for protecting vessels or systems connected thereto from reaching overpressure conditions. The terms "structure(s)" and "container(s)" are used herein to broadly mean any apparatus, assembly or device for containing fluid pressure which includes a fluid pressure rupturable portion or part, e.g., rupture disks, rupture disk assemblies, aerosol and other containers for containing pressurized fluids, cases such as battery cases containing materials which can develop pressure upon overheating, etc.
A large variety of rupturable pressure relieving apparatus of the rupture disk type have been developed and used. Generally, these devices include a rupture disk supported between a pair of complementary supporting members or flanges which are connected to a relief connection in a vessel or system containing fluid pressure. When the fluid pressure within the vessel or system exceeds the design rupture pressure of the disk, the disk ruptures causing fluid pressure to be relieved from the vessel or system through the ruptured disk.
The rupture disks which have been previously used have taken various forms and have included one or more parts. For example, flat rupture disks, rupture disks including domed or concave-convex central portions, and composites of such disks and other components such as vacuum supports, modular support assemblies, cutting members, etc. have all been used. Rupture disks with concave-convex central portions in which the concave side of the disks are exposed to fluids under pressure are commonly known as "conventional" rupture disks. Conventional rupture disks are placed in tension by the force of the fluids under pressure exerted thereon and rupture occurs when the tensile strength of the disk material is exceeded. Rupture disks including concave-convex central portions in which the convex side of the disk is exposed to fluid pressure are known as "reverse buckling" disks. Reverse buckling disks are placed in compression by the fluid pressure and, typically, the concave-convex portion first reverses itself and then ruptures when an overpressure condition occurs.
Knife blades have been utilized with reverse buckling rupture disks to puncture the disks upon reversal and bring about the full opening thereof. Scores or grooves have been utilized in both conventional and reverse buckling rupture disks to create lines of weakness along which the disks rupture when overpressured.
Rupture pressure relieving fluid containers are described in U.S. Pat. No. 4,576,303 issued May 18, 1986. The containers each include a substantially frustum-shaped indentation formed in a wall or other portion thereof and at least one score formed on a part of the indentation. When a predetermined fluid pressure is exerted on the indentation, it inverts and tears along the score whereby a portion of the wall or part containing the indentation is opened and fluid pressure is relieved therethrough.
While the various prior rupturable pressure relieving apparatus (collectively referred to as "rupture disks") have been successfully used in a large number of applications, problems are still encountered. One such problem is fragmentation of the rupture disk, i.e., pieces of the rupture disk fragment or sever from the assembly and may contaminate and/or damage the processes and/or equipment into which the fragments are carried. U.S. Pat. No. 5,005,722, which is assigned to the assignee of the present invention and which is incorporated herein by reference for purposes of disclosure, discloses a hinge member which extends into the concavity of a reverse buckling rupture disk in alignment with the mouth or open side of a C-shaped scoreline. When the disk ruptures in the reverse direction, the petal created by the C-shaped scoreline wraps around the hinge. The hinge thereby prevents fragmentation of the petal. U.S. Pat. No. 4,211,334, which is assigned to the assignee of the present invention, discloses a catcher bar which extends across the concavity of a reverse buckling disk in order to catch the severed portion of the ruptured disk.
Although the hinge member and catcher bar have been successful in reducing fragmentation of pressure relieving apparatus, problems remain. It is contemplated that these problems arise from the symmetrical shapes of the concave-convex "domes", frustums, and the like (hereinafter collectively referred to as "indentations") of the prior apparatus. It is impossible to predict at what point on a symmetrical indentation inversion (reverse buckling) of the indentation will begin; and, concomitantly, where such inversion will begin with respect to any scores, knife blades, or other rupture causing mechanisms or the fragmentation reducing hinges, catcher bars, and the like. Since inversion normally propagates across the indentation from the initiation point, if the initiation point is unknown it is impossible to predict the direction from which the inversion will approach the rupture causing mechanism and/or fragmentation reducing mechanism in the prior assemblies. Therefore, it is impossible to predict where rupture will begin. This affects both the rupture pressure and the ability of the device to rupture without fragmentation. For example, in a typical reverse buckling disk having a C-shaped score, the inversion may begin at a point 90.degree. away from the mouth/hinge area of the C-shaped score and the direction of approach of the inversion may cause tearing of the hinge area in the mouth of the C-shaped score.
Therefore, there is a need for apparatus and method which will allow predetermination and control of the inversion initiation point or face on an inverting, rupturable, pressure relieving apparatus.